The Video Phone (VP) service is defined in 3G as a data service based on 64 k Unrestricted Data Information (UDI). It enables both parties of a call to see pictures shot by the video camera of the opposite terminal. The 64 k data service multiplexes video data, audio data, and control data. Each type of information occupies one logical channel, that is, the video data occupies video logical channel, the audio data occupies audio logical channel, and the control data occupies control logical channel.
Monitoring is a means provided for national security persons including policemen, army men, and the persons working in national security department, which enables these persons, if they know the telephone numbers used by criminals or suspects in advance, to notify the exchange of these numbers so as to obtain the communication content of the monitored number. In this way, security persons can know the status of criminals or suspects when the criminals or suspects dial a call or do other things, such as transmitting and/or receiving short message, turning on the phone, turning off the phone or updating location.
The existing monitoring is based on the voice. When the criminals or suspects are making a call, the exchange transmits the audio data duplicated during the call to the monitoring centre. Generally, the contents of the call are transmitted to a phone of a designated telephone number.
Since the monitoring is significant to national security, it has been used by many countries currently as one of the requirements for an exchange accessing a network. For the national security persons, they are not satisfied with simple voice monitoring. Especially with the increasing pervasiveness of VP, the opportunity of criminals and the like using VP is greatly increased. Therefore, video monitoring is in urgent need, which monitors the pictures shot by the video camera of the opposite terminal during the call to further obtain more visual information, such as geographical location, picture of person, and so on, in which the security persons are more interested.